An investigation into hop fractions leading to hoppy aroma in beer.

Abstract
Aroma hops have been fractionated in several ways. A series of pilot scale brews were made in which each of the aroma hop fractions was substituted for the last hopping in proportion to its abundance in the starting hops. Bitterness was adjusted with isomerised hop extract. Some compounds which do not readily steam distil from whole hops contribute to the hoppy flavour of beer. Virtually all of the hoppy flavour appears to be derived from hop oil obtained by 24 hour steam distillation of neutral fraction, where most of all hop volatile compounds measured in beer originate. Heating of the neutral fraction does not lead to an enhancement of the hoppy flavour. Some hop oil compounds are more easily lost when added to kettle in ethanol solution rather than in leaf hops or hop pellets. It may be possible to obtain greater hoppy flavour from a given hop preparation by adding it slightly later in the process than the point where aromatic leaf hops or hop pellets would normally be added. In practical fermentation it appears that while beer with hoppy character can be made with the use of extracted hop oil, it is difficult to duplicate the hoppy flavour of an existing product produced by adding leaf hops or hop pellets in any other way.
Keywords : aroma brewing fermentation hop extract hop oil hop pellet hops